1. Field of the Invention
The invention relates to a telescopic lifting assembly that includes two antiparallel juxtaposed linear drives connected functionally one behind the other in the direction of actuation and having an inner component extending upward relative to an outer component during actuation, especially for the purpose of hydraulic height adjustment of a medical treatment table by means of linear drives in the form of pressure actuated cylinder/piston arrangements.
2. The Prior Art
In the classical design of such arrangements, a plurality of pneumatic or hydraulic cylinder/piston arrangements are most often provided which are inserted concentrically into one another whereby the piston rod of an outer unit is hollow and forms directly the cylinder for the following unit. The individual cylinder/piston arrangement can be biased with a pressure medium parallel and simultaneously or individually or one after the other as well. Depending on the number of parallel phases working in the same direction, the total lifting height can be a multiple of the longitudinal extension of the lifting assembly relative to its retracted state. Such lifting assemblies are used for various purposes such as for elevating platforms, tables adjustable in height, as in the case of the above-mentioned medical treatment tables or the like. Similar designs are also disclosed in WO 94/05583, for example, whereby the individual drives are always connected from one inner component to the following outer component.
The above-described multiphase lifting assemblies inserted into one another have various disadvantages in terms of the pressure medium connection to or between the individual phases, the guiding and sealing means, the prevention against twisting and similar occurrences despite the small basic height compared to the total achievable lift whereby it is sufficient that the achievable lift is equal to the double amount of the individual stroke lengths which is achieved by means of two antiparallel juxtaposed linear drives. Arrangements of the aforementioned type are being presently used and have the advantage that they can be realized by constructing them in small dimensions and with common linear drives without difficulties, such as commercially available hydraulic cylinder/piston arrangements. For example, surgical tables with such telescoping lifting assemblies are disclosed in CA 24 34 996 A1, US 2002/144349 A1, U.S. Pat. No. 5,431,087 or DE 33 28 908 A1, whereby the two antiparallel cylinder/piston arrangements are in communication with the two cylinders juxtaposed in reverse order and which remain relatively stationary thereby in the center between the outer coupling points of the piston rod, which means practically in the center of the lifting assembly. The outer surfaces of the cylinders are thereby interconnected. The inner components act upon different parts. The connected cylinders travel halfway with the stroke that extends at the other end of the lifting assembly. In these known arrangements it is particularly a disadvantage that the two piston rods, which are extending relatively far outwardly, must be either constructed very sturdy or have additional separate guides to make corresponding total lifting heights possible so that no problem can occur in terms of lateral tilting or twisting, especially in case of lifting heavy loads. These additional measures cause such lifting assemblies to be again relative spacious in their construction which limits free footage under the table, especially in the mentioned use for the adjustment of medical treatment tables.
It is the object of the present invention to improve a telescopic lifting assembly of the aforementioned type in such a manner that the mentioned disadvantages of the known arrangement are avoided and that secure and stable guiding of the lifting assembly is ensured in an especially simple and space-saving manner even in case of heavy loads.